As shown in FIG. 1, the 3GPP EPS comprises an E-UTRAN (Evolved Universal Terrestrial Radio Access Network), an MME (Mobility Management Entity), an S-GW (Serving Gateway), a P-GW (Packet Data Network Gateway), an HSS (Home Subscriber Server), a 3GPP AAA server (3GPP Authentication, Authorization, and Accounting server), a PCRF (Policy and Charging Rules Function entity) and other support nodes. Wherein the S-GW is an access gateway device in connection with the E-UTRAN, used for forwarding data between the E-UTRAN and the P-GW, and responsible for caching call waiting data; the P-GW is a border gateway between the EPS and a PDN (Packet is Data Network), and responsible for accessing the PDN and forwarding data between the EPS and the PDN, etc.; and the PCRF is connected to an operator's IP (Internet Protocol) service network through an Rx interface to obtain service information.
The EPS supports intercommunication with a non-3GPP network. The intercommunication with the non-3GPP network is implemented through an S2a, S2b, or S2c interface, while the P-GW is used as an anchor point between the 3GPP network and the non-3GPP network. The non-3GPP network is categorized into a trusted non-3GPP network and an untrusted non-3GPP network. The IP access of the trusted non-3GPP network may be connected to the P-GW directly via the S2a interface; the IP access of the untrusted non-3GPP network needs to be connected to the P-GW via an ePDG (evolved packet data gateway), and the interface between the ePDG and the P-GW is S2b. A UE (User Equipment) may also be connected to the P-GW directly via the S2c interface according to a DSMIPv6 (Dual Stack Mobile Ipv6).
In the EPS system, a PCEF (Policy and Charging Enforcement Function entity) resides in the P-GW, and the PCRF and the P-GW exchange information via a Gx interface. When the interface between the P-GW and the S-GW is based on a PMIPv6, the S-GW also has policy control function, which is called BBERF (Bearer Binding and Event Reporting Function entity), and the S-GW and the PCRF exchange information via a Gxc interface. When the UE accesses the EPS through the trusted non-3GPP network, the BBERF also exists in the trusted non-3GPP access network, and the trusted non-3GPP network access gateway and the PCRF exchange information via a Gxa interface. An AF (Application Function) providing service for the UE sends service information for setting a PCC (Policy and Charging Control) or Qos (Quality of Service) policy to the PCRF via the Rx interface.
An MIPv6 (Mobile IPv6) supports the accessibility and continuity of sessions while an MN (Mobile Node) moves in the network by binding an IPv6 care-of address (CoA) and an IPv6 home address (HoA) of the MN. However, since the IPv6 network has not been deployed widely, the IPv4 network will still be prevalent for a long term in the future. The MN in the IPv6 network always moves to a network not supporting IPv6, thus it is compulsory to expand the MIPv6. An effective solution is the DSMIPv6, which is a client-based MIP and requires both the MN and home agent to support the DSMIPv6. In the EPS system, the P-GW supports the home agent function. The MN supporting the DSMIPv6 supports mobility over the IPv4 or IPv6 network by binding the IPv4/IPv6 CoA and IPv4/IPv6 HoA.
The EPS system supports multi-PDN access, i.e., the UE may access multiple PDNs simultaneously via multiple P-GWs or one P-GW. FIG. 2 shows a scenario of a UE accessing two PDNs simultaneously through two P-GWs according to the DSMIPv6.
FIG. 3 shows a flow chart of a UE initiating attachment to and accessing two PDNs based on the scenario in FIG. 2, specific steps are as follows.
Step 301: a UE accesses a trusted non-3GPP access network via layer 2, and an HSS/AAA performs access authentication and authorization to the UE.
Step 302: after the authentication is successful, a connection of the UE to layer 3 of the trusted non-3GPP access system is established, and the trusted non-3GPP access system assigns an IP address to the UE as a CoA of the UE.
Step 303: the trusted non-3GPP access network sends a gateway control session establishment request message to a PCRF, and the message includes an NAI (Network Access Identifier) of the UE and the CoA of the UE.
Step 304: the PCRF sets a control policy based on a network policy and subscription information of the UE, i.e., a QoS rule, and provisions it to a BBERF in the trusted non-3GPP access network through an acknowledge gateway control session establishment message, and the control policy here has no relation to the service which the UE is about to access.
Step 305: the UE queries a DNS (Domain Name Server) according to an APN1 (Access Point Name) to obtain an IP address of a P-GW1 capable of accessing a first service network, and a security association is established between the UE and the P-GW1, during this process the P-GW1 assigns an HoA1 to the UE.
Step 306: the UE sends a binding update request message to the P-GW1, and the message includes the CoA and the HoA1.
Step 307: the P-GW1 sends indication of an IP-CAN (IP Connectivity Access Network) session establishment message to the PCRF, and the message includes the CoA, HoA1, NAI and APN1; and the PCRF associates the IP-CAN session with the gateway control session according to the CoA.
Step 308: the PCRF, according to the network policy, user subscription information and information about the first service network to be accessed, etc., sets a corresponding PCC rule and event triggers, and sends them to the P-GW1 via an acknowledge IP-CAN session establishment message.
Step 309: a PCEF in the P-GW1 installs the PCC rule and the event triggers provisioned by the PCRF, and returns a binding acknowledgement message to the UE.
Step 310: the PCRF, according to the network policy, the user subscription information and the information about the first service network to be accessed, etc., sets a QoS rule; if this QoS rule is different from the QoS rule set in step 304, QoS rule is updated, and the new QoS rule is provisioned to the BBERF in the trusted non-3GPP access network through a gateway control and QoS rule provision message; the PCRF also sets event triggers and sends them to the BBERF via the gateway control and QoS rule provision message.
Step 311: the BBERF in the trusted non-3GPP access network installs the received event triggers, and returns an acknowledge gateway control and QoS rule provision message to the PCRF.
If the updated QoS rule is provisioned, the BBERF also needs to update the installed QoS rule.
Till now, the UE attachment flow is complete, and an IP-CAN session to a PDN1 is established.
Step 312: because of service requirement, the UE determines to access a second service network, and queries the DNS according to an APN2 to obtain an IP address of a P-GW2 capable of accessing the second service network.
Step 313: a security association is established between the UE and the P-GW2, during this process the P-GW2 assigns an HoA2 to the UE.
Step 314: the UE sends a binding update request message to the P-GW2, and the message includes the CoA and the HoA2.
Step 315: the P-GW2 sends an indication of IP-CAN session establishment message to the PCRF, and the message includes the CoA, HoA2, NAI and APN2; and the PCRF associates the IP-CAN session with the gateway control session according to the CoA.
Step 316: the PCRF, according to the network policy, user subscription information and information about the second service network to be accessed, etc., sets a corresponding PCC rule and event triggers, and sends them to the P-GW2 via an acknowledge IP-CAN session establishment message.
Step 317: a PCEF in the P-GW2 installs the PCC rule and the event triggers provisioned by the PCRF, and returns a binding acknowledgement message to the UE.
Step 318: the PCRF, according to the network policy, the user subscription information and the information about the second service network to be accessed, etc., sets a QoS rule and event triggers, and provisions them to the BBERF in the trusted non-3GPP access network through a gateway control and QoS rule provision message.
Step 319: the BBERF in the trusted non-3GPP access network installs the received QoS rule and the event triggers, and returns an acknowledge gateway control and QoS rule provision message to the PCRF.
Through the above-mentioned flow, the UE establishes IP connection to the first service network and IP connection to second service network, respectively. This IP connection from the UE to the service network is called IP-CAN. For the convenience of description, hereinafter, the IP connection from the UE to the first service network is called a first IP-CAN session, and the IP connection from the UE to the second service network is called a second IP-CAN session. The PCRF always stores the latest PCC rule, QoS rule and event triggers for each IP-CAN session related to the UE. According to a UE identification included in an IP-CAN, it may be determined that this IP-CAN session is an IP-CAN session related to the UE. Both the IP-CAN session and the gateway control session are implemented by a diameter session when they are between these network elements. A diameter session established between the PCRF and the trusted non-3GPP access network is called a gateway control session, or a Gxx session (in the prior art, this connection is established according to a diameter protocol, and the context of the diameter session is stored in the PCRF and the trusted non-3GPP access network). A diameter session established between the P-GW1 and the PCRF or between the P-GW2 and the PCRF, is called a Gx session.
The PCRF provisions the QoS rule and the event triggers, which are used to perform policy and charging control to the first IP-CAN session, to the BBERF in the trusted non-3GPP access network through the Gxx session between the trusted is non-3GPP access network and the PCRF; and it provisions the PCC rule and the event triggers, which are used to perform policy and charging control to the first IP-CAN session, to the PCEF in the P-GW1 through the Gx session between the P-GW1 and the PCRF. Likewise, the PCRF provisions the QoS rule and the event triggers, which are used to perform policy and charging control to the second IP-CAN session, to the BBERF in the trusted non-3GPP access network through the Gxx session between the trusted non-3GPP access network and the PCRF; and it provisions the PCC rule and the event triggers, which are used to perform policy and charging control to the second IP-CAN session, to the PCEF in the P-GW2 through the Gx session between the P-GW2 and the PCRF.
However, if the event triggers are provisioned according to the above-mentioned flow, the BBERF cannot correctly report trigger events customized by the event triggers.